In recent years, it has been greatly required that rigid disc drive devices, like other devices, be small-sized, and high-density recording on recording media has become an important problem. Accordingly, magnetic discs of the thin metal film type having a high coercive force (Hc) have been developed for use in place of those of the conventional oxide-coated type.
On the other hand, as magnetic heads for hard discs, floating-type magnetic heads are in use which comprise a slider having the face to be opposed to the recording medium and a core chip incorporated in the slider. It has been proposed to provide a core chip of the so-called MIG type (metal-in-gap type) especially in floating-type magnetic heads for use with rigid discs of the thin metal type. The core chip of the MIG type includes a film of Sendust, amorphous magnetic alloy or like highly saturated magnetic flux material formed by sputtering and opposed to the magnetic gap portion of the chip (see, for example, Unexamined Japanese Patent Publication SHO 62-295207).
FIG. 11 is a plan view of a MIG-type core chip fabricated according to the present invention for use with rigid discs, to show the magnetic gap portion in its face to be opposed to the recording medium. As far as the structure appearing on the medium opposed face is concerned, the core chip has the same construction as known MIG-type core chips.
More specifically, the core chip 4 comprises a pair of core segments 1a, 1b made of Mn-Zn ferrite and butting against each other, and a thin film 2 of ferromagentic metal such as Sendust and a gap spacer 3 of SiO.sub.2 or the like. The core chip 4 is secured to a slider (not shown) with bonding glass portions 5, 5 to provide the floating-type magnetic head.
Such floating type magnetic heads have heretofore been produced by the process illustrated in FIGS. 32 to 41.
First, two base plates of Mn-Zn ferrite are prepared, both surfaces of each of the base plates are polished to a mirror finish, and the first of the base plates, 6a, is coated on its upper surface (gap forming surface) with a thin ferromagnetic metal film 2 and then with a gap spacer 3 of a thickness corresponding to the desired gap length by sputtering as shown in FIG. 32. A plurality of precut grooves 7 are formed at a given pitch P in the upper surface (gap forming surface) of the second base plate 6b to obtain ridges with a preliminary track width t.sub.1 slightly larger than the desired track width as shown in FIG. 33.
Next as shown in FIG. 34, a plurality of winding grooves 8 are formed in the gap forming surface of the second base plate 6b, and the two base plates 6a, 6b are fitted together with their gap forming surfaces opposed to each other. Further as seen in FIG. 35, glass bars 9 are inserted into the respective winding grooves 8, then melted and solidified, filling the precut grooves 7 with glass 10 as shown in FIG. 36 and giving a block 11 composed of the pair of base plates 6a, 6b bonded together with the glass.
Next, the block 11 is cut into a plurality of core blocks 14 along broken lines A-A'. A plurality of truck width defining grooves 12 are cut at a predetermined pitch in the head portion of each core block 14 to form a plurality of medium facing ridges 13 having the desired track width t.sub.2 as shown in FIG. 37.
The core block 14, when sliced, affords core chips 4 each comprising a pair of core segments 1a, 1b, a thin ferromagnetic metal film 2 and a gap spacer 3 as seen in FIG. 38.
Next, sliders 16 as shown in FIG. 39 are prepared which are made of a nonmagnetic ceramic such as calcium titanate, each core chip 4 is fitted in a slit 15 formed in the slider 16, and a glass plate 17 having a lower softening point than the glass bar 9 is placed on the core chip 4 as shown in FIG. 40.
The glass plate 17 is thereafter melted and solidified, thereby filling the glass 5 into the spaces at opposite sides of the medium facing ridge 13 and into the clearance in the slider slit 15 around the core chip 4 and bonding the core chip 4 to the slider 16. Finally, the slider 16 is chamfered as at 18 to finish the exterior, whereby a floating-type magnetic head is completed as shown in FIG. 41.
In preparing the conventional magnetic head by the above process, the upper surface of the base plate 6a of Mn-Zn ferrite is coated by sputtering with the thin ferromagnetic metal film 2 which is different from the Mn-Zn ferrite in coefficient of expansion in the step of FIG. 32, with the result that the base plate 6a warps during sputtering due to a change in temperature to create a great error in the gap length of the magnetic gap portion finally obtained.
In the steps of FIG. 34 through FIG. 36, moreover, the SiO.sub.2 film and the ferrite base plate, which are not satisfactorily wettable with glass, are bonded together with glass to fabricate the block 11. Consequently, the block 11 is very low in bond strength and is likely to fracture or crack in the subsequent step. The core chip 4 eventually obtained is also low in the strength of bond between the core segments 1a and 1b.
Further in bonding the two base plates to each other with glass, the glass bar 9 needs to be heated to a temperature about 150.degree. to 250.degree. C. higher than the softening point (e.g., 590.degree. C.) of the glass. This permits a reaction to proceed at the interface between the ferrite base plate and the thin Sendust film, possibly forming a quasi-gap or a secondary gap at the interface.
Additionally, the step of FIG. 32 wherein the upper surface of the first base plate 6a is coated with the thin ferromagnetic metal film 2 by sputtering gives rise to the problem that sputtered metal particles disturb the crystallinity of the first base plate surface owing to the resulting impact or the like, consequently forming a nonmagnetic amorphous layer at the interface between the first base plate 6a and the metal film 2 for the amorphous layer to provide a secondary gap.